Telephone centeal station



(No Model.) 10 Sheets-Sheet 1. G. D'ADHEMAR. TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

INVENTOH WITNESSES.

(No Model.) 10 Sheets-Sheet 2.

G. DADHEMAR.

TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

W/ TNE SSE S INVENTOH E O ,Fzrzns co. wmoumo" \wsumcrcm. o c

(No Model.) 10 Sheets-Sheet 3.

G. DADHEMAR.

TELEPHONE CENTRAL STATION.- No. 540,012. Patented May 28, 1895.

Emir- INVENTO/P Z K/ w W/TNESSES:

m: NGHMS Pnens co, PNOTO-UTHQ, wnsnmmon. u c

(No Model.) 10 Sheets-Sheet 4.

G. DADHEMAR.

TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

W/TNESSES.

(N0 Model.) 10 Sheets-Sheet 5.

G. DADHEMAR. TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

x" /'NVENTOR A TTOH E Y8.

(No Model.) 10 Sheets-Sheet 6.

G. DADHEMAR.

TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

o f; af@ Q o 7 A TTOHNE Y8.

m: uonms PETERS co. vucroumov, WASHINGYON. a c.

(No Medal.) 10 Sheets-Sheet 7.

G. DADHEMAR.

TELEPHONE CENTRAL STATION.

N0x 540,012. Patented May 28, 1895.

I;IVIIIVIIVI;IVIIIIVIIIII 7 lNVENTOf? WITNESSES.

ATTOI? EYS (No Model.) 1o Sheets-Sheet a. G. DADHEMAR.

TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

i s ij Y I I I I j I I a] WITNESSES." a M/VENTOH gwwhm B) E Z V A770NEYS.

(No Model.) 10 Sheets-Sheet 9. G. DADHEMAR. TELEPHONE CENTRAL STATION.

No. 540,012. Patented May 28, 1895.

% mvavroa WWcJA B) i ATT EYS.

w t w h S k M e h S m R A M E H D D G (No Model.)

TELEPHONE CENTRAL STATION.

Patented May 28, 1895.

. u x 1 I Z I Z M a /.Z 0 1 2 V F W Z 1 Q y fill! \//I 0 Z 1 Z w 7 F n i4 F v 1 0 Z Z n L 7. a Z 3 a wL m 1 N/ H z 1 Z Z 7 I/|1 l/ Z f I F}, \A!F Z E 1/ I w v AOL Z a Z 1 L p 1 IL X /NVENTO/? BY ATT 5Y8 UNITED STATESPATENT OFFICE.

GASTON DADIIFMAR, OF PARIS, FRANCE.

TELEPHONE CENTRAL STATION.

SPECIFICATION forming part of Letters Patent No. 5 0,012, dated May 28,1895.

Application fi ed June ,1894- Serial No. 515,150. (No model.) Patentedin France May 10, 1893, No. 230,380.

To a, whom it nutty concern.-

Be it known that I, GASTON DADHEMAE, a citizen of the Republic ofFrance, residing at Paris, in said Republic of France, have inventedcertain new and useful Improvements in Telephone Central Stations, (forwhich Letters Patent were granted to me in France, No. 230,380, datedMay 10, 1893, and a certificate of addition thereto, dated December 28,1893,) of which the following is a specification.

This invention relates to certain improvements in telephone centralstations and apparatus for the same, by which a greater number ofsubscribers can be connected with each station and attended to withgreater facility by a smaller number of employs than the telephonecentral stations heretofore in use, and theinvention consists ofatelephonecentral station which comprises primarily, an improvedannunciator, a switch board arranged below said annunciator and providedwith rows of jacks having metallic sockets and contact springs,separated by insulating blocks, a local circuit connected with saidjacks and containing an electro-magnet, the armature of which cuts outthe electro-magnet of an ann unciator while the line is occupied, saidlocal circuit also acting on the telephone of the operator at the momentof calling in such a manner that no electric communications can takeplace between the telephones of the different operators.

The invention consists, further, in the construction of the plugs bywhich the connection with the subscribers jacks is established, next inthe construction of a combined key for conversation and listening, andin the combination of the latter with the calling-up keys, an inductioncoil, a relay and a local circuit, as will be fully describedhereinafter and finally defined in the claims.

The general object and nature of my invention being thus indicated, Iwill now proceed to describe particularly the different apparatus ofwhich my improved central station is composed and the circuits by whichsaid apparatus are connected and by which they are operated in practice.

In the accompanying drawings, Figure l is a perspective view of myimproved telephone central station with its annunciators, jacks, plugs,and keys, and showing the relative position of the operator to thestation and the receiving and transmitting telephones. Figs. 2, 2,2",and2are diagrams showingthe different apparatus which compose my improvedtelephone central station and the circuits connecting them with eachother and with the lines of the subscribers. Fig. 3 is a side elevation,drawn on a larger scale, of an annunciator by which the number of thesubscriber who desires to communicate with another subscriber isindicated. Fig. 3 is a detail front view of an annunciator-drop. Fig. 4is a vertical longitudinal section of a portion of the switch board,showing a plug inserted into one of the jacks. Fig. 4 is a plan of Fig.l; Fig. 4, a front view of the perforated front plate for the jacks.Figs. 5 and 5 represent, respectively, a side elevation and a verticallongitudinal section of one of the plugs used with the jacks in myimproved central station, said figures being drawn on a larger scale.Fig. 6 is a sectional side elevation showing one of the plugs in aposition of rest when not connected with a subscribers line. Fig. 7 is aside elevation of the multiple-wire connection by which the line ofevery subscriber is connected with the central station. Figs. 7 and 7are details of Fig. '7. Fig. Sis a diagram showing the local circuitsfor each jack. Figs. 9 and 10 are respectively a side elevation and avertical transverse section of the compound key by which the operatormakes or establishes connection, and Figs. 11, 12, and 13 are verticallongitudinal sections showing the three different positions into whichthe compound key can be placed for making proper connections.

Similar letters and figures of reference indicate like parts in all thedrawings.

The annunciator is arranged above the switch-board, and in such aposition that any drop can be'readily seen and read by the operator. Anannunciator is arranged for each subscriber, and provided with a drop,carrying number of the subscriber. The annunciator and its drop areshown in detail in Figs. 3 and 3 and it consists of an electromagnet A,which is attached to an upright plate B at the upper front part of thestation, and of an armature (L, which is pivoted at Z) and provided witha forward-extending rod 0, that moves with the armature. In front theplate 19 and which carries a contact-screw of the plate B is pivoted atd to suitablelugs e, a piece f, g, h, to the lower end of which isattached a drop 2', which is formed of a convex plate of metal'and onwhich is engraved or otherwise produced, the number of one of thesubscribers, as shown in Fig. 3*. The piecef, g, h, is so balanced onits pivot 01, that it assumes, when released, the position shown indotted lines in Fig. 3, in which position the number on the drop 1', isexposed to view. The piece f, g, it, however, is held ordinarily in theposition shown in full lines in Fig. 3 by the rod 0, which engages theupper endf, of said piece and retains thereby the drop in its inwardposition so that its face is covered by the forward projectionbracket-plate j, which is attached to the f rontplate B. A secondelectro-magnet K is attached to the front-plate B, belowtheelectromagnet A and provided at its rear-end with an armature 7a,which is pivoted at Z and provided with a forward-extending arm m,

the front-end of which is located below the projecting nose g of thepiece f, g, h. A plate n, of hard rubber or other suitable insulatingmaterial, is attached to the armature k and provided with an openingwhich is engaged by a spring 0, that is attached to a plate 19. Adjacentto the upright plate p .is arranged a plate g, which is insulated from7' against which the spring 0 abuts when in a state of rest. One end ofthe coils of the electro-magnet A is connected with'a binding-screw onthe upright plate 19, while the other end of said coils is connectedwith a line-wire, the plate q being connected by-a binding-screw withthe second line-wire of a subscriber. The coils of the electro-inagnet Kare connected with a local circuit, which will be described hereinafter.

By the action of the magneto-call of the subscriber the electro-magnet Ais excited, and its armature a attracted, so that the rod 0 is raisedand the piece,f, g, h, permitted to turn on its axis, whereby the drop2', on which the number of the subscriber is arranged, is moved forwardbeyond the bracket-plate j, so as to be seen by the operator. The rod 0is stopped by a contact-screw s, which is supported by an insulated lugattached to the front-plate B, as shown in Fig. 3, and which screwcloses the local circuit of a call-bell. On the other hand, when acurrent is passed through the coils of the electro-magnet K, itsarmature 1c is attracted so that the forwardly-extending rod m of thesame engages the nose g of the piecef, g, 72, so as to return it intoits initial position, the numbered drop 11, being likewise moved andcovered by the bracket-plate j. The plate 12, which connects thearmature 7a with the spring 0, moves the spring 0, away from thecontact-screw 'r, cuts the electromagnetAout of the circuit of thesubscribers line, and returns the armature a and rod 0 into their formerposition. As soon as the current ceases in the electro-magnet K, its

armature k, and rod m are returned into their .former position under theaction of the spring 0, so that the latter again forms contact with thecontact-screw o while the piecef, g, h, is retained in its normalposition by the contact of the rod 0, with its upper endf. If desired, asecond spring'o, and contact-screw 1" may be used without changing thegeneral arrangement described, so as to produce in the same manner, thethrowing in or out of circuit of the second line wire of theelectro-magnet A.

It is most advantageous to arrange the annunciators above theswitch-board, so as to have as much place as possible available for thejacks, which have to be arranged as conveniently as possible to thehands of the operator. By this arrangement of the annunciators, thenumbers of the subscribers are conveniently visible to the eye of theoperator, without requiring any change of position of the head. It isalso possible to arrange, while preserving the position of the drops ofthe annunciators, to render the numbers visible to the operator by meansof inclined mirrors, which are arranged in front of the operator, so asto reflect in the direction of the eyes of the same, when sitting infront of the switch-board, said mirrors reflecting the number of anyannunciator-drop as shown in Fig.

1. In this case,however, the number has to be inscribed on the drop inreversed figures, so as to appear in its proper position in the mirror.By this arrangement, the operator can give all her attention to theproper supervision of the jacks on the manipulating table.

The connecting-plug.0ne of the connecting-plugs is shown as insertedinto a jack in Fig. 4, and inside elevation and in longitudinal sectionrespectively in Figs. 5 and 5. It consists of a metallic tube 1, intoone end of which is screwed a hollow cylindrical piece 2, which inclosesan insulating tube 3 that surrounds a metallic tube 4, which is againseparated bya second insulating tube 5, from the central cylindrical rodor core 6 of metal. A tube 4, is screwed into the front-end of a piece7, the rear end of which is perforated and connected by a screw 9, withthe terminal tube ofa flexible conducting cord, in which the conductingwires are arranged. The central rod 6, is screwed into a metalliccylinder 10, in which another conducting wire of the flexible cord islirtnly held by a screw 11. Onto the opposite end of the rod 6, isscrewed a cylindrical piece of metal 12, which forms the terminal of theinterior conductor of the flexible cord. its middle portion, so as topermit the insertion of the screws 9 and 11. This opening is closed by asleeve 14, which is securely held in position by the screw 15. Theflexible cord contains an interior conductor of fine wire, whichterminates in the piece 10 and which is covered by an insulating layerof suitably prepared silk or cotton. Around the central wire a secondconductor is formed by suitably The tube 1, has an opening at- IIOcovered conducting wires, which terminate in the small tube 8, and whichare likewise covered by an insulating layer of suitably prepared silk orcotton. The two insulated c011- ducting wires are arrangedconcentrically to each other and pass freely through the opening of thepiece 13, and then through a flexible tube or cover 16, formed of ahelicallywound wire, which is again covered by a braided layer of silk,cotton or linen. The exterior coiled wire 16 forms a conductor, whichterminates in the body of the plug and which is placed thereby inelectric connection with the tubes 1 and 2.

The jttc7cs.-The plugs are inserted into a series of jacks, which areshown in vertical section in Lin plan in Fig. 4:", while Fig. 49, is afront-view of the front-plate of a double series of jacks. Each jack iscomposed of a metallic socket to, which is connected with abackwardly-extending metallic plate 1') to which the conducting wire issoldered and of two metallic springs, c, d, which are made of unequallength and which are separated by a block 6 of hard rubber or othersuitable insulating material. The different parts are supported on abracket f, g, h, which is made of hard rubber or other insulatingmaterial, and in general form of the letter T, and which carries tworows of jacks, which are symmetrically arranged on the T-shaped bracketand which permit the grouping of a large number of jacks incomparatively small space. The corresponding pieces of the second row ofjacks are indicated by the same letters as those of the first row. Thesprings c and d are attached to the lower part of the T-shaped bracketby means of screws 2" and j, which are insulated from the springs byplates 71; and short tubes Z and m of hard rubber or other suitableinsulating material. The backwardly-extending plates 1) are retained inplace and insulated from the springs c d by the blocks 6' and plates is.

I11 Fig. 4, a plug is shown as being inserted into one of the jacks, sothat the tube 2 of the plug is in contact with the socket a, the tube twith the contact-spring c and the piece 12 of the plug with the spring dof the jack.

In Fig. 7, are shown the arrangements of a number of star-shaped plateswhich are mounted on a supporting cylinder, said plates having threearms each, to which the wires for the common jacks and the wires of thejacks used for replying, are attached. Fig. 7, shows an end-elevation ofa group of three star-shaped plates and Fig. 7 a single detached plate.These star-shaped plates are punched from suitable metal and locked bymeans of akey to the supporting rod on which all plates are assembled,as shown in Fig. 7, a suiiicient number being arranged so that the wiresconnected thereto can be united into one cable. Theinterior rod iscovered with an insulating sleeve (1 on which are placed alternately thestar-shaped plates d and the separating collars d which are retained onthe sleeve 61 by the key d which engages notches in the sleeve, platesand collars, as shown in Figs. 7and 7. The three star-shaped plates ofeach group on the supporting rod 61 are shifted relatively to eachother, so that they assume the position shown in Fig. 7, whereby thestringing of the wires for each group of plates d is greatlyfacilitated.

In Fig. 8, is shown the electric connections of the metallic circuit ofa subscriber with the common jacks on the dilferent switchboards I, II,III, N, of a central station, the replying jackRand the annunciator A.The two wires of the metallic circuit of a subscriber are connected withthe springs c and (V of the different jacks and are then connected withthe annunciator, one of the wires passing to the contact e f which iscontrolled by an electro-magnet D The sockets a of the diiferent jacksof the same circuit are connected with each other and with theelectromagnet 13*, which latter is connected with one pole of a battery8*, while the other pole is connected with the body of the plug,asindica-ted at h Fig. 8. In the switch-board on which the annunciatorand the replying-jack are arranged together with the circuit justdescribed, the connection of the three wires of the replying jack withthe three wires of the common jacks is made by a group of star shapedplates, arranged on the cylinder M, as before described. The two wires,which come from the station of the subscriber are connected either withthe springs of the jack on the switch-board I, or with those of theswitchboard N, the extremities being selected for this connection sothat the wires can readily be extended to new switch-boards in case suchshould be necessary. The battery B consists of primary or secondarycells and may be replaced by any other source of electricity, by

which the current for all the different local circuits of the station issupplied in such a manner, that all the electro-magnets, such as D areconnected at IV with one pole, while the other pole of the battery isconnected at X with the body of the plugs. hen a plug such as h isinserted into a jack, the local circuit of the battery is closed and thecurrent passes from the battery through the plug to the socket a or thejack and to the electromagnet D The armature of the electro-magnet D isattracted, the contact is broken at e and the annunciator A is placedout of circuit during the time that the plug remains inserted in thejack. As soon as the plug is withdrawn, the armature of theelectromagnet D is dropped and the contact c f is re-established, sothat the annunciator A is replaced in the circuit of the subscriber. InFig.8, for the sake of clearness the two wires of the metallic circuitof the plug arenot shown, but they are shown in Fig. 2 and will bedescribed later on.

lhelocalcircuit, the ell'ect of which on the electro-magnet D has justbeen described, is also combined with other accessories in the IIOcentral station, which forms a testing circuit that is entirelyindependent of the telephone of the operator.

The combined conversing and listening key.-Figs. 9 to 13 showthe'construction of the combined key for conversing and listening. Fig.2 shows the relative position of the combined conversing and listeningkeyto the other parts of the station. .Fig. 13 shows the position of thekey when in its normal position of rest; Fig. 11, when it is set forconversation, and Fig. 12, when it is set for listening; the last threefigures showing merely the difierent positions of the key so as torender its operation clearer. The lever Z is keyed to a square pivot Zto which is also applied a block Z which carries two concentric pivots Zand Z At the lower part of the key-frame is arranged a movableinsulating block Z", to which are attached two pairs of flatswitchsprings Z and Z the block being open in its center part andcarrying a transverse pin Z The insulating block Z is guided in itsvertical movement on two pins Z which are attached to the transverseinsulating bottompiece Z of the key-frame. Two pairs of helical springsZ arearranged at opposite sides of the block Z and exert a tension onthe block, which holds the same in the position shown in Figs. 9 and 10,the lower ends of the springs being attached to bindingposts Z and Z atthe under side of the insulatingbar Z The current passes from thebindingposts Z and Z, by means of connecting-screws Z and Z to therespective switch-springs. A connecting-strap Z is applied at its upperend to the pivot Z while its lower slotted end enters into the centralopening of the block Z and is engaged by the fixed transverse pin Z. Asecond connecting-rod or strap Z is formed of two pieces of exactly thesame shape as the strap Z said pieces being applied to the pivot Z ofthe block Z while their lower slotted ends are extended into the centralopening of the movable block Z and are likewise engaged by the fixedtransverse pin Z. The connecting-strap Z is provided with alaterally-extending pin Z which serves to raise a contact-spring Z whichis attached at one end to theinsulated block Z and the free end of whichforms contact with a stud Z on the insulating-block Z Theconnecting-strap Z carries a similar pin Z which forms contact with acontactspring Z which is attached to the insulatingblock Z The pins Zand Z are connected by their straps Z and Z, plug Z and lover Z with themetallic supporting-plate of the keys, said plate being electricallyconnected with the pole w of the battery B The lever Z which is providedwith a knob or button Z is retained in the position of rest, shown inFig. 13, by the tension exerted on the connecting-straps Z and Z by thehelical springs Z By taking hold of the button Z of the lever Z andmoving the same over into the position shown in Fig. 11, theconnectingrod Z is lifted, owing to the movement of the pivot Z inupward direction so that the block Z together with the switch-springs ZZ is raised and at the same time the pin Z forms contact with the springZ. The connecting-strap Z is moved in a downward direction following theoscillating motion of the block Z but without exerting any specialeffect. As the pivot Z is moved beyond the dead-center of the axis ofthe lever, Z, the lever is retained in the position shown in Fig. 11,until it is returned into the position shown in Fig. 13.

In passing the lever Z from the position shown in Fig. 13, to theposition shown in Fig. 12 or into the listening position, the inverseeffect is produced namely, the connect' ing-strap Z is raised, also theblock Z with its switch-springs, while simultaneously the pin Z makescontact with the spring Z and presses the latter in contact with thestud Z but as the position for listening is necessary only for a moment,it is not necessary to move the pivot Z beyond the dead-center of theaxis of the lever Z, so that as soon as the lever Z is released, it isreturned again into the normal position shown in Fig. 13.

The diagrams, Figs. 1, 2, 2 and 2 show the application of the key incombination with the circuits, which participate in the functioning ofthe ditferent parts. By the contact-spring Z and the disposition of therelay Q, the armature of which carries an insulated contactspring I)that abuts on a contact-point b and by the combination of the listeningand conversation keys into one member, a single relay only is required,and thereby the construction of the central station considerablysimplified. In Fig. 2, the combined key Z is shown in the position ofconversation. P shows the plug of the calling subscriber, and P the plugof the subscriber that is called up. Fig. 2, shows further theconnections of the different members of the central station. y and 2indicate the connecting-jacks of two subscribers yfland 2. They areconnected with similar jacks on the other switch-boards, as was beforedescribed. g is the special jack required for replying to the subscribery, which is connected by means of the starshaped plates M with the wiresof the common j acks, A is theannunciator of the subscriber y and K itslocal electro-inagnet. The special jack of the subscriber y and hiscorresponding annunciator are supposed to be located on anotherswitch-board. P is the plug of the calling subscriber and P the plug ofthe subscriber called up, which is placed into its normal position ofrest, on the table below the switch-board. The flexible cords of theplugs aremade in the usual manner and are held on proper tension byweighted pulleys (not shown) which move over the cords. For each pair ofplugs such as P and P is required a combined conversation and listeningkey Z, an annunciator P for indicating the end of the conversation, witha local electro-magnet P. This latter is made of exactly the sameconstruction as the local electro-magnet K of the annunciatorA, but isnot provided with a contact-spring.

Each operator attends to a certain number of pairs of plugs,with acombined conversation and listening key, a pair of calling-up keys V and'u, a telephone-receiver T, an inductioncoil t a microphone-transmitterS and a local relay Q. The calling-up keys V and '0 are similar inconstruction, their construction and arrangement being clearlyunderstood from the diagram, Fig. 2, in which the key t; is mountedabove a supplementary contactplate f which is not necessary for the keyV.

The induction-coil 25 comprises three coils, the coil g for thetelephone, the microphonecoil h and the testing-coil i". The latter isalways in open circuit except in the moment when the line alreadyoccupied is tested. A resistance r is placed in the circuit of thelatter coil for weakening the current. to and 50 are the wires of theprimary or secondary battery, dynamo or other source of electricity B,which supplies by branch-wires the necessary current. for theelectro-maghet ot' the annunciator P for indicating the end of theconversation and for the local relay Q. The poles of the calling batteryare indicated by the letters 711 and 11".

Figs. 2, 2, 2 and 2 show the diiterent positions of the circuits duringthe four operating stages. In each of these figures the circuits of twosubscribers only are shown for the purpose of simplifying thedescription. It is understood, however, that each subscriber has ageneral jack in each table and a special jack and a calling-annunciatorin one of the sections.

Referring to Fig. 2 it is assumed that the subscriber y has called whichis indicated by the annunciator A. The operator then places the plug Pinto the jack 1 This produces the current from the pole m of the battery13 that passes through the body of the plug P to to the socket of thejack y and from the same to all the corresponding jacks in the othersections. The current passesthen to the electro-magnet K which isexcited and then back to the other pole w" of the battery 13. Thearmature of the electro-magnet K is attracted, the contact 0, rinterrupted and thereby the coil of the calling-electro-magnet A placedout of circuit. The operator sets then the key Z into position forconversation, takes the plug P and touches with its core the socket ofthe jack .2 of the subscriber 2 called up. The line of the subscriber 2thus called upon is shown as being already occupied in Fig. 2.Consequently in this figure the body of the plug P connects the socketof the jack .2 with the pole zt of the battery B". Likewise in Fig. 2,the current of the battery enters into the core of the plug P, passesover the conversation-key Z, the calling-key o, the arma ture a and thecontact Z) to the relay Q, then over the inducting-coils 2'", theresistance-coil T the supporting-plate ot the calling key, thesupporting-plate of the conversation-key and over the wire (1 to thepole to of the battery B The passage of the current to the inductingcoil 2' induces a current in the coil g which passes into thetelephone T and produces a signal or click in the same.

It is obvious that if no plug is pressed into the jack of the subscriberZ, the socket of all corresponding jacks are cut off from the pole x ofthe battery, so that at the moment of touching the socket no currentpasses through the plug P',so that the telephone remains silent andindicates thereby that the line is free.

In Fig. 2, the operator having ascertained that the jack Z of thesubscriber Z is free, forces the plug P into the jack, so as toestablish communication with the subscriber 6. This figure shows themoment when in pressing down the keyo the subscriber Z is called up,which has the effect that the current of the battery m 72 is sentthrough the plug P, while at the same time by the contact mf, theelectro-magnet Qis cut out of circuit, the current passing the pole 20of the battery B" over the wire 61, the supporting-plates of theconversation and calling-keys, over U,f and the coils of theelectro-magnet Q to the'pole 0c of the battery B". This causes thearmature Ct to leave the contact I) and make contact with c. From thismoment the core of the plug P does not communicate any more with theinduction-coil 2'" but with the core of the plug P. It is clear that assoon as the contact of the key o with the plate f isinterrupted, thearmature a remains still attracted, as the contacts 6 12 close a newcircuit for the current, which passes from the pole 00 over the coils ofthe relay Q, contacts b b and over the contact Z Z to thesupporting-plate of the key Zand over the wire d back to the pole 20.Therefore duringthe conversation of the operator with the subscribers Zand 6, all parts remain in the positions described. It is obvioushowever, that as soon as the operator returns the key Z into itsvertical position or position of rest, the contacts Z and Z areinterrupted and the current does not pass any more through the coils ofthe relay Q, so that the armature a leaves the contact 0 and drops backagainst the contact 1). This latter position is shown in Fig. 2" wherethe two subscribers 7 and 8 are in communication and in which theapparatus of the operator is cut out from the circuit of communicationbetween the subscribers. In this position the cores of the plugs P and Pare in direct communication with the contact l of the conversation-keyand in addition thereto the annunciator P which indicates the end of theconversation, is in communication in the usual manner with the plugs Pand P.

When the annunciat-or P indicates the end of the conversation, theoperator verifies this signal P is eifaced. From the contact Z thecurrent passes through the coils of the relay Q to the pole 00", so thatthe armature a is at tracted and placed against the contact a, andthereby direct communication bet-ween the cores of the plugsPand P isestablished. The operator then replaces the key Z into its position ofrest, by which the contacts 1 ,1 and Z are separated. The current canthen neither pass over P nor ever the coils of the relay Q, so that thearmature leaves the contact c and returns to the contact I) by theaction of its spring. It results from the foregoing description that itis not necessary to make any connection between the testing cir-.

cuit and the earth, so that in consequence thereof the metallic circuitsof the subscribers do not influence each other, nor is there anyinterfering noise that would impair the conversation. Further as thecircuits of the telephones of the ditferent operators have no connectionwith each other nor with the earth, these devices are entirelyindependent from each other and are not subject to any disturbance orconfusion of sounds.

Having thus described my invention, I claim as new and desire to secureby Letters Patent 1. In a telephone central station, the combination,with a calling-annunciator of an electro-magnet, a local circuit forsaid electromagnet, and means for automatically breaking the circuit ofsaid electro-magnet of the arinunciator and at thesame time returningthe drop of said annunciator, substantially as set forth.

2. In a telephone central station, the combination, with acalling-annunciator, of an electro-magnet in local circuit with saidannunciator, means for automatically breaking the circuit of saidelectro-magnet and returning the drop of the annunciator, a plug formedof three concentric conductors, and ajack composed of a socket that isalways isolated from the line and earth and two insulatedcontactsprings, substantially as set forth.

3. In a telephone central station, the combination of two series or rowsof jacks, composed of a double row of sockets, two rows ofcontact-springs arranged back of said sockets, and separating blocks ofinsulating material provided with enlarged heads at their inner endsextending between the contactsprings of each row, and an insulatingbracket arranged to support both rows of jacks, one

above and the other below said bracket, substantially as set forth.

4. In a telephone central station, the combination with a group of threestar-shaped connecting-plates, shifted relatively to each other on theirsupporting axle, each plate being connected with the three wires in asubscribers circuit, of jacks, composed each of a metallic socket, apair of contact-springs and an insulating block for separating saidcontact-springs,- and plugs formed of three concentric conductors,substantially as set forth.

5. In a telephone central station, the combination, of a combinedconversation and. listening key, provided with two. pairs of auxiliarycontacts, a local circuit connected with said auxiliary contacts, arelay in said local circuit, an armature for said relay provided with aninsulated extension-arm, contacts for said armature and arm, andelectric connections between said auxiliary contacts, the armature andits contacts, whereby the armature is attracted when the key is set forconversation or listening but dropped into normal or initial positionwhen the key is placed into its position of rest, substantially as setforth.

6. In a telephone central station, the com bination with the calling-upkeys and the telephone of the operator, of a local circuit, a relay insaid circuit, a pair of connecting-plugs of which the core of the plugof the subscriber called-up is in connection with the armature of therelay which. armature is normally in said local circuit, and a specialtesting coil located in the induction-coil of the microphonean'disolated from the line and earth, said armature being switched out ofsaid local circuit when the relay is operated and connected with thecore of the plug of the calling subscriber, substantially as set forth.

7. In a telephone central station, the combination of a combinedconversation and listening key, having two pairs of auxiliary'con-'tacts, a key for the subscriber to be called up,

an auxiliary contact-plate for said calling-up key, a relay, an armaturefor said relay having an extension-arm, a local circuit which comprisessaid auxiliary contacts, the coils of the relay and the contact-plate,contacts for the armatureof the relay, and two connecting plugs,respectively for the calling and called-up subscribers, said auxiliarycontactplate closing the local circuit, so as to connect the cores ofthe plugs and attract the armature of the relay until theconversationkey is returned from its position of conversation orlistening into its position of rest, substantially as set forth. p

In testimony that I claim the foregoing as my invention I have signed myname in presence of two subscribing witnesses.

GASTON DADHEMAR. Witnesses:

' PAUL GoEPEL,

K. R. BRENNAN.

ITO

IIC

